Question

Describe the lines of defense associated with the immune system. Your description should include:

1. Four examples of anatomical barriers

2. Three of the primary mediators of inflammation

3. Names and brief descriptions of the four features that the specific immune system exhibits  

4. Name the two cell types known as lymphocytes and name their origin and maturation locations.   

5. Then, indicate how the cell mediated response (T cells) is activated.

Answer 1

Immunity is defined as the capacity of the body to resist pathogenic agents. It is the ability of body to resist the entry of different types of foreign bodies like bacteria, virus, toxic substances, etc.
Immunity is of two types: I. Innate immunity.
II. Acquired immunity.
INNATE IMMUNITY OR NON-SPECIFIC IMMUNITY
Innate immunity is the inborn capacity of the body to resist pathogens. By chance, if the organisms enter the body, innate immunity eliminates them before the development of any disease. It is otherwise called the natural or non-specific immunity.
This type of immunity represents the first line of defense against any type of pathogens. Therefore, it is also called non-specific immunity.
ACQUIRED IMMUNITY OR SPECIFIC IMMUNITY
Acquired immunity is the resistance developed in the body against any specific foreign body like bacteria, viruses, toxins, vaccines or transplanted tissues. So, this type of immunity is also known as specific immunity.
It is the most powerful immune mechanism that protects the body from the invading organisms or toxic substances. Lymphocytes are responsible for acquired immunity.
Types of Acquired Immunity
Two types of acquired immunity develop in the body: 1. Cellular immunity
2. Humoral immunity.
Lymphocytes are responsible for the development of these two types of immunity.
DEVELOPMENT AND PROCESSING OF LYMPHOCYTES
In fetus, lymphocytes develop from the bone marrow . All lymphocytes are released in the circulation and are differentiated into two categories.
The two categories are:
1. T lymphocytes or T cells, which are responsible for
the development of cellular immunity
2. B lymphocytes or B cells, which are responsible for
humoral immunity.
T LYMPHOCYTES
T lymphocytes are processed in thymus. The processing occurs mostly during the period between just before birth and few months after birth.
Thymus secretes a hormone called thymosin, which plays an important role in immunity. It accelerates the proliferation and activation of lymphocytes in thymus. It also increases the activity of lymphocytes in lymphoid tissues.
B LYMPHOCYTES
B lymphocyte  were first discovered in the bursa of Fabricius in birds, hence the name B lymphocytes. Bursa of Fabricius is a lymphoid organ situated near the cloaca of birds. Bursa is absent in mammals and the processing of B lymphocytes takes place in liver (during fetal life) and bone marrow (after birth).

Cell-mediated immunity is defined as the immunity developed by cell-mediated response. It is also called cellular immunity or T cell immunity. It involves several types of cells such as T lymphocytes, macrophages and natural killer cells and hence the name cell mediated immunity. Cell-mediated immunity does not involve antibodies.
Cellular immunity is the major defense mechanism against infections by viruses, fungi and few bacteria like tubercle bacillus. It is also responsible for delayed allergic reactions and the rejection of transplanted tissues.
Cell-mediated immunity is offered by T lymphocytes and it starts developing when T cells come in contact with the antigens. Usually, the invading microbial or non-microbial organisms carry the antigenic materials. These antigenic materials are released from invading organisms and are presented to the helper T cells by antigen-presenting cells.